An exemplary embodiment of this application relates to ink jet printing by a print head having partial nozzle redundancy for the purpose of compensating for failed or malfunctioning nozzles. More particularly, an exemplary embodiment relates to an ink jet printer having print head with partial nozzle redundancy that ejects ink droplets from all of the nozzles while printing, but is operated at less than maximum available droplet ejection throughput. The print head nozzles are checked for malfunctioning, and the printing to be performed by any detected malfunctioning nozzle is compensated for by nearby nozzles that have their droplet ejection throughput increased to provide additional droplets.
Droplet-on-demand ink jet printing systems eject ink droplets from print head nozzles in response to pressure pulses generated within the print head by either piezoelectric devices or thermal transducers, such as resistors. The ejected ink droplets are propelled to specific locations on a recording surface, commonly referred to as pixels, where each ink droplet forms a dot or spot thereon. The print heads have arrays of droplet ejecting nozzles and a plurality of ink containing channels, usually one channel for each nozzle, which interconnect an ink reservoir in the print head with the nozzles.
In a typical piezoelectric ink jet printing system, the pressure pulses that eject liquid ink droplets are produced by applying electric pulses to the piezoelectric devices, causing bending or deforming to pressurize the volume of liquid ink in contact therewith. When a voltage pulse is applied to a selected piezoelectric device, a quantity of ink is displaced from the ink channel and a droplet of ink is mechanically ejected from the nozzle associated with that piezoelectric device. Just as in thermal ink jet printing, the ejected droplets are propelled to pixel targets on a recording surface to form an image of information thereon. The respective channels from which the ink droplets were ejected are refilled by capillary action from an ink supply. For an example of a piezoelectric ink jet printer, refer to U.S. Pat. No. 6,739,690 or U.S. Pat. No. 3,946,398.
As is well known, there are two basic ink jet printing configurations; viz., printing an image on an intermediate surface (usually a drum) for subsequent transfer to a recording medium and printing an image directly on a recording medium. For each of these two basic configurations, there are ink jet architectures for printing the image in a single pass or printing the image in multiple passes. For multiple pass architectures, the same pixels can be addressed multiple times or each pixel can be addressed only once. For each of the single and multiple pass architectures, the print head may scan the print head over the image receiving surface to print the image or the recording medium may be scanned past a print head while the print head prints the image thereon. Additionally, the print head may scan in one direction or scan bi-directionally. It is the intent of this application for the print head disclosed herein to apply to any of the above architectures for which the same pixels can be addressed only once.
Ink jet printing technologies suffer from reliability concerns where individual droplet ejecting nozzles can fail or malfunction on a print head. The failure of a single nozzle generally can force the replacement of an entire print head. Most nozzle failures are caused by external contamination, such as contaminants in ink or manufacturing debris and the nozzle failures are generally proportional to print throughput, so the higher the printing volume, the more likely a nozzle will fail. The result of a single failed nozzle can require the replacement of a print head because the resulting missing line or column of pixels is visually objectionable. There have been many attempts in the ink jet industry to compensate for missing nozzles without having to replace the print heads. Examples of ink jet printers having systems that compensate for missing or malfunctioning nozzles without the need of replacing the print heads are disclosed below.
US Patent Publication Nos. 20050105105 and 20050116981 disclose a printer, a computer program, and a method to camouflage defective print elements in a print head having a plurality of print elements.
U.S. Pat. No. 4,907,013 discloses means and circuitry for detecting a malfunctioning nozzle in an array of nozzles in the ink jet print head. If the printer processor is unable to compensate for the malfunctioning nozzle by stepping the print head and using non-malfunctioning nozzles during subsequent passes over the print medium, the printer is shut down.
U.S. Pat. No. 4,963,882 discloses using multiple nozzles per pixel location. In one embodiment, two ink droplets of the same color are deposited upon a single pixel location from two different nozzles during two passes of the print head. A failure of one of the two nozzles printing each pixel does not prevent at least some color for each pixel, so that totally missing pixels are prevented.
U.S. Pat. No. 5,581,284 discloses a method for identifying any failed nozzle in a full width array print bar of a multicolor printer and substituting at least one droplet from a nozzle in another print bar having a different color of ink. The substitute fill in with a droplet having a different color of ink prevents a missing spot in the printed information, so that print bar replacement is avoided.
U.S. Pat. No. 5,640,183 discloses a number of droplet ejecting nozzles are added to the standard column of nozzles in a nozzle array, so that a number of redundant nozzles are added at the ends of each column of nozzles. The print head is shifted regularly or pseudo-randomly such that a different set of nozzles prints over the first printed swath during a subsequent pass of the print head in a multi-pass printing system.
U.S. Pat. No. 6,215,557 discloses a system for identifying faulty ink jet nozzles in an ink jet print head based upon evaluation of a test pattern printed by the print head. The system generates a faulty nozzle record and the printer controller or printer driver alters the print data to print the desired image using only good nozzles.
U.S. Pat. No. 6,695,435 discloses a method for selectively printing a pixel at a print location having a missing color caused by a failed or impaired nozzle in a print bar of a multicolor printer. The method includes determining which colors are to be printed based on a color value for the missing color pixel and selecting at least one color in the place of the missing color pixel based on a pseudo-random process. The color of some neighboring pixels may be changed to include a combination of colors that include the missing color.